Electromagnetic switching device having a discharge gap formed by two spaced coaxial lines extending into a gas-filled waveguide



May 9, 1967 I LARSON 3,319,114

ELECTROMAGNETIC SWITCHING DEVICE HAVING A DISCHARGE GAP FORMED BY TWO SPAGED COAXIAL LINES EXTENDING INTO A GAS-FILLED WAVEGUIDE Filed Jan. 9, 1964 VOLUME INVENTOR Rodger G. Larson BY, v E

ATTORNEY VOLUME WITNESSES:

JED :3 W

3,319,114 ELECTROMAGNETIC SWITCHING DEVICE HAV- ING A DHSCHARGE GAP FORMED BY TWO SIAQED CUAXIAL LINES EXTENDING INTG A GAS-FILLED WAVEGUIDE Rodger G. Larson, Brooklyn, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 9, 1964, Ser. No. 336,707 15 Claims. (Cl. 31539) The present invention relates to switching devices for high frequency electromagnetic energy, and more particularly to devices for switching electromagnetic energy in coaxial transmission lines.

It is an object of the invention to provide a device for rapidly switching high frequency electromagnetic energy from one section of transmission line to another.

A further object is to provide such a device that is small in size and light in weight.

Another object is to provide such a device that has a long operating life.

Still another object is to provide such a device that has broad band operating characteristics.

Yet another object is to provide a device for switching electromagnetic energy rapidly and efficiently from one section of coaxial transmission line to another.

A further object is to provide a device for rapidly switching electromagnetic energy between one coaxial line and either one or the other of second and third coaxial lines that are connected to form a T-junction.

The foregoing objects as well as other objects and advantages of the present invention are achieved by a switching device that comprises a cut-01f attenuator that is formed by a hollow Waveguide, means for sealing in the hollow waveguide a gas at a pressure of the order of 100 millimeters of mercury, first and second coaxial transmission lines having inner conductors that extend into the gas within said hollow waveguide to form a gap that is long enough so that electromagnetic energy is substantially attenuated and reflected by the attenuator before the energy can be transferred between the transmission lines, and means for applying to said gap a switching voltage to produce a discharge across said gap and make a low-attenuation path for efiiciently transferring electromagnetic energy between the transmission lines. A conductive'ring encircles the gap. The ring serves as a control electrode for applying a biasing potential to the gap and can also serve as an impedance matching element.

The details of the present invention will become more apparent from the following description of the accompanying drawing wherein:

FIGURE 1 is a partially schematic illustration, in lon gitudinal section, of a device that is provided in accordance with the present invention for switching electromagnetic energy between two coaxial transmission lines; and

FIG. 2 is a partially schematic illustration, in longitudinal section, of a device in accordance with the present invention for switching electromagnetic energy within a T-junction for coaxial transmission lines.

Referring to FIG. 1, there is illustrated a switching device comprising a hollow waveguide 11 that forms a cut-01f attenuator for high frequency electromagnetic energy in the TM hollow'waveguide mode, a pair of dielectric elements 13 and 15 for scaling in waveguide 11 a noble gas such as argon or argon with water vapor at a pressure of the order of 100 millimeters of mercury, and a pair of input and output coaxial transmission lines 17 and 19. Coaxial transmission line inner conductors 21 and 23 pass through the elements 13 and 15, respectively, and extend coaxially into the gas within the hollow Umted States Patent O ce Patented May 9,

waveguide. There is a space or gap between the ends of conductors 21 and 23. The inner conductor 21 is connected to a DC. ground as is schematically shown in FIG. 1.

The outer conductors of the coaxial transmission lines 17 and 19 and the conductor that forms hollow waveguide 11 have cylindrical cross sections. The diameters of these conductors are equal. An R.F. input, not shown, supplies high frequency electromagnetic energy in the principal TEM mode to the transmission line 17. An R.F. lo'ad, not shown, is connected to the output end of the transmission line 19.

A conductor 27 is supported within and insulated from the inner conductor of the coaxial line 19 by suitable insulator means such as a glass coating, not shown, for applying a voltage across the gap between the conductors 21 and 27. One end of conductor 27 extends slightly into the gap between the ends of the inner conductors 21 and 23. The other end of conductor 27 passes through the outer conductor of the coaxial transmission line 19 and is connected to a source of switching voltage, not shown. An insulator 31, mounted within a short tubular conductor 33 extending from a hole in the outer conductor of the transmission line 19, supports the conductor 27.

A conductive ring 35 encircles the gap between the ends of the inner conductors 21 and 23. The ring 35 is used principally to apply a biasing potential to the gap and also is used for impedance matching purposes. The ring 35 is supported by an annular insulating septum 37 that is positioned in coaxial relationship with conductors 21 and 23. The septum 37 is supported by the inner wall of the hollow waveguide 11. A conductor 39 connects the ring 35 to a source of biasing voltage, not shown. An insulator 41, mounted within a short tubular conductor 43 extending from a hole in the cylindrical wall of waveguide 11, supports the conductor 39.

In operation, if no switching voltage is supplied to conductor 27 and if the coaxial transmission line 17 is energized with high frequency electromagnetic energy at a frequency that is below cut-off for propagation in the hollow waveguide 11, the electromagnetic energy is reflected by waveguide 11 back into the transmission line 17 and also is attenuated by waveguide 11. Thus,'no energy is transferred between the transmission lines 17 and 19. In this condition the switching device keeps electromagnetic energy from being supplied to the RF. load, not shown.

If an alternating or direct switching voltage of the order of a few hundred volts relative to ground is supplied to conductor 27, a discharge in the form of a column that has characteristics known as a brush discharge is produced across the gap between conductors 21 and 23. The brush discharge has a diameter that is of the order of the diameter of the coaxial line inner conductors 21 and 23. The discharge does not widely diffuse in the gas volume at the relatively high gas pressure that is used. At the moment the discharge occurs, a lowattenuation current path is produced around which electromagnetic energy H lines close for efiiciently transferring electromagnetic energy in a coaxial line mode between the transmission lines 17 and 19. Thus, electromagnetic energy is supplied with relatively low attenuation to the RF. load, not shown.

The conductive ring 35 is a control element that is used to shape the electromagnetic field to confine the brush discharge into a column. The bias voltage that is applied to ring 35 is of the order of volts negative with respect to ground, for example. This voltage is adjusted for a maximum negative value that will not maintain a glow discharge, i.e., a discharge that fills the gas volume instead of being confined to a brush discharge.

3 The size and position of ring 35 are chosen to improve the efficiency of the energy transfer by helping to preserve a constant characteristic impedance along the transmission line that is formed by coaxial lines 17, 19 and the section of coaxial line that is completed by the brush discharge. The ring 35 is non-resonant.

At the moment the switching voltage is removed from conductor 27, the discharge across the gap between conductors 21 and 23 cease to exist and the switching device is restored to the condition where electromagnetic energy is kept from the RP. load. The biasing potential applied to ring 35 helps to restore the switching device rapidly back to the last-described condition by removing ions from the discharge area.

The optimum values for the gas pressure within waveguide 11, the switching voltages and the bias voltage are determined best by experiment. A high value of gas pressure is important to ensure that a brush discharge is produced.

The switching device is very useful in a'pulsed system, for example. A switching pulse of DC. voltage or low frequency AC. voltage is applied to the conductor 27 simultaneously or slightly in advance of a pulse of high frequency electromagnetic energy supplied to the coaxial transmission line 17. The switching pulse causes a brush discharge of high ionization density to occur in the discharge gap between conductors 21 and 27. Under these conditions the pulse of high frequency electromagnetic energy is transferred between the coaxial transmission lines 17 and 19 with relatively low attenuation. After the application of the pulse of electromagnetic energy, the switching pulse is removed. The switching device recovers very rapidly to prevent transfer of electromagnetic energy between the transmission lines 17 and 19 until the next switching pulse is received.

Another embodiment of the invention is illustrated in FIG. 2. Here there is shown a T-junction that connects the outer conductors 51, 53 and 55 of three coaxial transmission lines. One part of the T-junction is a hollow waveguide 56 that forms a cut-off attenuator for electromagnetic energy in the TM hollow waveguide mode.

Coaxial line inner conductors 57 and 59 extend coaxially into the waveguide 56 and are spaced apart. Coaxial line inner conductor 61 extends into the space between conductors 57 and 59 at right angles therewith to form a first discharge gap between conductors 61 and 75 and a second discharge gap between conductors 61 and 77. The inner conductor 61 is connected to a D.C. ground as is shown schematically in FIG. 2.

A plurality of dielectric elements 67, 69 and 71 support the inner conductors 57, 59 and 61, respectively, within the waveguide 56. Elements 67, 69 and 71 also seal within waveguide 56 a gas at a pressure of the order of 100 millimeters of mercury. A further dielectric element 73 extends transversely across the center of the waveguide 56 to divide the volume of gas into two parts that contain the first and second discharge gaps, respectively.

Switching voltage conductors 75 and 77 are supported within and insulated from the conductors 57 and 59, respectively, by suitable insulating means, not shown. A conductive ring 81 encircles the gap between the conductors 57 and 61. A conductive ring 83 encircles the gap between the conductors 59 and 61. A conductor 85 is connected to both of the rings 81 and 83 for supporting the rings and for applying biasing potentials to the two gaps. The rings 81 and 83 are slanted, the adjacent ends of the inner conductors 57 and 59 are cross cut on a bias, and the end of the inner conductor 61 is rounded for shaping the electromagnetic field. The rings 81 and 83 also serve as non-resonant impedance matching elements to improve the efficiency of the transfer of electromagnetic energy across the gaps.

In operation of the switching device shown in FIG. 2, if no switching voltages are supplied to conductors 75 and 77 and if the input coaxial transmission line is energized with high frequency electromagnetic energy at a frequency that is below cut-ofi for propagation in the hollow waveguide 56, substantially none of the energy is transferred to either one of the output coaxial transmission lines 51, 57 and 53, 59. In this condition the switching device keeps electromagnetic energy from being transferred to either one or the other of R.F. loads, not shown.

If a switching voltage of the order of a few hundred volts relative to ground is supplied to either one of conductors 75 and 77, a brush discharge is produced either across the gap between conductors 61 and 75 or across the gap between conductors 61 and 77. The discharge completes the inner conductor of a coaxial transmission line system for transferring electromagnetic energy with relatively low attenuation to either one of the RF. loads depending upon which one of conductors 75 and 77 carries a switching voltage. Upon removal of the switching voltage, the discharge across the gap ceases to exist and the switching device is restored rapidly to the condition where electromagnetic energy is prevented by the device from reaching the RF. load.

While the invention has been shown in but two forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various additional changes and modifications without departing from the spirit and scope of the invention.

What is claimed is:

1. A switching device for high frequency electromagnetic energy comprising a hollow waveguide that is dimensioned below cut-off for the electromagnetic energy to be switched, a first transmission line having a conductor that extends into said hollow waveguide, a sec-0nd transmission line having a conductor that extends into said hollow waveguide and is spaced from the conductor of said first transmission line to form a gap, said hollow waveguide forming a cut-off attenuator between said first and second transmission lines, means for sealing a gas in the part of said waveguide that contains said gap, and means for ionizing said gas to produce a discharge across said gap to make a low-attenuation path for transferring electromagnetic energy between said transmission lines.

2. A switching device as it set forth in claim 1, wherein said gas is under a pressure of the order of millimeters of mercury to cause a brush discharge to form between said conductors of said first and second transmission lines at the moment said gas is ionized.

3. A switching device as is set forth in claim 2, further including a conductive ring that encircles said gap, the size and position of said ring being chosen to enhance the efficiency of the transfer of electromagnetic energy between said transmission lines.

4. A coaxial line switching device comprising a hollow Waveguide that is adapted to form a cut-off attenuator for electromagnetic energy to be switched, a first coaxial transmission line having an inner conductor that extends into said attenuator, a second coaxial transmission line having an inner conductor that extends into said attenuator and is spaced from the inner conductor of said first coaxial transmission line, and means for sealing a gas under a relatively high pressure within said hollow waveguide to form an ionizable discharge gap in the space between said inner conductors.

5. A coaxial line switching device as is set forth in claim 4, further including a conductive impedance matching ring encircling said gap.

6. A coaxial line switching device as is set forth in claim 4, wherein said hollow waveguide and the outer conductors of said coaxial transmission lines are joined in coaxial relationship.

7. A coaxial line switching device as is set forth in claim 4, wherein said hollow waveguide and the outer conductor of said first coaxial transmission line are joined in coaxial relationship, and said hollow wave guide and the outer conductor of said second coaxial transmission line are joined at right angles.

8. A coaxial line switching device as is set forth in claim 7, further including a third coaxial transmission line having an outer conductor joined in coaxial relationship with said hollow waveguide, the inner conductor of said third coaxial transmission line extending into said attenuator in spaced relationship with the inner conductor of said second coaxial line, and means for sealing a gas under a relatively high pressure within said hollow waveguide to form a discharge gap in the space between the inner conductors of said second and third transmission lines.

9. A switching device for high frequency electromagnetic energy comprising a hollow waveguide that is dimensioned below cut-oft for electromagnetic energy to be switched, means for sealing a gas within said waveguide, a first transmission line having a conductor that extends into the gas within said waveguide, a second transmission line having a conduct-or that extends into the gas within said waveguide to form a gap between said conductors, means for ionizing said gas to produce a discharge across said gap and to make a low-attenuation path for transferring electromagnetic energy between said transmission lines, and a conductive ring encircling said gap.

10. A switching device as is set forth in claim 9, wherein said transmission lines comprise first and second coaxial lines that are at right angles with each other, a third coaxial line that is coaxially aligned with said first coaxial line, the inner conductors of said first and third coaxial line being spaced from the opposite sides of the inner conductor of said second coaxial line to form two gaps, the outer conductors of said first and third coaxial lines being joined to said hollow waveguide, and means for dividing said hollow waveguide into two separate gas sealed compartments that contain said two gaps, respectively.

11. A switching device as is set forth in claim 9, wherein the gas that is sealed within said hollow waveguide has a pressure of the order of 100 millimeters, whereby the discharge of said gas is in the form of a column.

12. A switching device for high frequency electromagnetic energy comprising a cut-off attenuator that is formed by a hollow waveguide that is dimensioned below cut-off for electromagnetic energy to be switched, means for sealing a gas under a relatively high pressure within a section of said waveguide, a first high frequency transmission line having a conductor that extends into said section, a second high frequency transmission line having a conductor that extends into said section, said condoctors being spaced apart to form a discharge gap, an impedance matching ring that encircles said gap within said hollow waveguide, and means for selectively applying a relatively high switching voltage across said gap for producing a discharge in the form of a column having thecharacteristics of a brush.

13. A switching device as is set forth in claim 12, wherein said ring is conductive, and means for applying a bias voltage to said ring for shaping the field of electromagnetic energy to confine the discharge to said column and for removing ions from said discharge gap.

14. A coaxial line switching device comprising coaxial inner and outer conductors, said inner conductor being interrupted to form a gap, said outer conductor in the vicinity of said gap forming a cut-off waveguide attenuator, further coaxial inner and outer conductors, said further outer conductor being joined to said first-mentioned outer conductor to form a T-junction, said further inner conductor extending into said gap to divide said gap into two parts, means for sealing each of said gap parts to form two gas filled chambers, and an insulated electrode contained within portions of the first-mentioned inner conductor on opposite sides of said gap parts for applying separate switching voltages to said gap parts, respectively, for independently ionizing said two gas filled chambers.

15. A device for switching high frequency electromagnetic energy comprising a section of hollow waveguide that is dimensioned below cut-off for electromagnetic energy to be switched, means for sealing a gas under a pressure of the order of millimeters of mercury within said section of hollow waveguide, a first coaxial transmission line having an inner conductor that extends into the gas within said section of hollow waveguide, means for connecting the inner conductor of said first coaxial transmission line to a DC. ground, a second coaxial transmission line having an inner conductor that extends into the gas within said section of hollow waveguide, the inner conductors of said first and second coaxial transmission lines being spaced apart within said hollow waveguide to form a gap, a control element formed by a ringshaped conductor that encircles said gap, means for insulating said element from said hollow waveguide and from said inner conductors, a further conductor supported by and insulated from the inner conductor of said second coaxial transmission line, means for applying a bias voltage relative to said D.C. ground to said control element, and means for applying a switching voltage of the order of several hundred volts relative to said D.C. ground to said further conductor to produce a brush ionization discharge between the inner conductors of said coaxial transmission lines.

References Cited by the Examiner UNITED STATES PATENTS 3,218,510 11/1965 Schulz 313-197 ELI LIEBERMAN, Primary Examiner.

PAUL GENSLER, Assistant Examiner. 

4. A COAXIAL LINE SWITCHING DEVICE COMPRISING A HOLLOW WAVEGUIDE THAT IS ADAPTED TO FORM A CUT-OFF ATTENUATOR FOR ELECTROMAGNETIC ENERGY TO BE SWITCHED, A FIRST COAXIAL TRANSMISSION LINE HAVING AN INNER CONDUCTOR THAT EXTENDS INTO SAID ATTENUATOR, A SECOND COAXIAL TRANSMISSION LINE HAVING AN INNER CONDUCTOR THAT EXTENDS INTO SAID ATTENUATOR AND IS SPACED FROM THE INNER CONDUCTOR OF SAID FIRST COAXIAL TRANSMISSION LINE, AND MEANS FOR SEALING A GAS UNDER A RELATIVELY HIGH PRESSURE WITHIN SAID HOLLOW WAVEGUIDE TO FORM AN IONIZABLE DISCHARGE GAP IN THE SPACE BETWEEN SAID INNER CONDUCTORS. 